1. Field of the Invention
The present invention relates generally to a medical device and protocols to facilitate diagnosis of Helicobacter pylori (H. pylori) based on administration of unlabelled urea.
2. Background of the Invention
Exhaled breath has long been known to enable non-invasive disease detection. Exhaled gases, such as ammonia, nitric oxide, aldehydes and ketones have been associated with kidney and liver malfunction, asthma, diabetes, cancer, and ulcers. Other exhaled compounds like ethane, butane, pentane, and carbon disulfide have been connected to abnormal neurological conditions. However, though analysis of body fluids (blood, sputum, urine) for disease diagnoses and monitoring is routine clinical practice, human breath analysis methodologies that exploit the non-invasive nature of such diagnoses are still under-developed and conventional technologies lack specificity, are excessively expensive or lack portability.
Sensors have been produced to measure gases in a variety of settings, including automotive and biological applications. See U.S. Pat. No. 7,017,389 to Gouma, the contents of which are incorporated by reference, regarding detection of Nox emissions in the automotive field. Technologies for monitoring exhaled breath require complex and expensive apparatuses that are difficult to calibrate and are often not sufficiently sensitive to provide a high degree of certainty in regard to medical condition diagnosis. Such biological systems pose challenges that include sensitivity to extremely low levels of gases, presence of reducing and oxidizing gases, organic vapors (VOCs), etc. See U.S. Pat. No. 7,220,387 to Flaherty et al., the contents of which are incorporated by reference, regarding disposable sensors to measure gaseous sample analytes.
A conventional apparatus disclosed by Kearney, D, et al., Breath Ammonia Measurement in Helicobacter pylori Infection, Digestive Diseases and Sciences, Vol. 47, No. 11, pp. 2523-2530 (2002), provides a fiber optic device placed in the stream of expelled breath that is connected to an optical sensor for detecting whether a patient has H. pylori by measuring for ammonia excreted by the lungs, utilizing a hydrophobic TFE-based membrane to avoid affect of dissolved ions such as ammonia. Also see, WO 03/041565 A2 of Hubbard et al., the contents of which are incorporated by reference, H. pylori detection.
Diagnostic tests for H. pylori include a) serologic testing to detect anti-H. pylori antibodies in blood, b) upper gastrointestinal endoscopy with mucosal biopsies, c) H. pylori culture, including antimicrobial susceptibility testing, and d) detection of H. pylori antigens in stool. Serologic testing, however, cannot distinguish current from old infection. Upper gastrointestinal endoscopic biopsies are submitted for rapid urease testing or histological examination, and this approach has the drawbacks of the invasive nature of endoscopy and the suboptimal performance of histopathology. H. Pylori culture is invasive and cumbersome and detection of H. pylori antigens in stool is limited by the low acceptance of stool testing and suboptimal specificity/sensitivity.
Several diagnostic tests are based on the ability of H. pylori to convert urea to CO2 and NH3 using its enzyme urease. H. Pylori produces large amounts of urease which often comprises about five percent of its total protein. Urease activity is assessed in two general ways: Biopsy-based rapid urease testing and various urea breath tests. Biopsy-based rapid urease tests require endoscopy for sample acquisition. Biopsy samples are placed in an agar gel or paper strip containing a pH indicator. In addition to requiring an invasive endoscopy, biopsy-based rapid urease tests provide a less-than-optimal test due to the time required for the diagnosis, which is 3-24 hours, a less than 90% specificity, and reduced sensitivity in children. Moreover, conventional devices, particularly point-of-care devices, are expensive, particularly to assess H. pylori, which discontinuously colonizes the gastroduodenal mucosa.
Conventional testing is performed utilizing instrumentation that ranges from variations of mass spectrometers to IR detectors that are costly and require a trained operator. Breath sample transportation is also an issue with most conventional devices. The limited availability of instruments operable by patients and available at the point of care requires samples to be shipped to central testing facilities, adding cost and inconvenience. In regard to Urea Breath Testing (UBT) for the diagnosis of H. pylori infection, there are two versions of the UBT, based upon the type of urea being used as a substrate: 13C labeled urea and 14C labeled urea. 14C is a radioactive isotope of carbon. 13C is a stable, non-radioactive isotope, encountered in nature. The FDA has approved both 13C- and 14C-based UBTs for the diagnosis of H. pylori, though the 14C-based assay is rarely used. The 14C-based UBT is associated with exposure to radioactivity, which albeit small for an otherwise healthy adult, is nevertheless present and patients should not be exposed to it in the absence of safe alternatives. It is because of the risk associated with the radioactivity of the 14C-urea that the 14C-based UBT is contraindicated in pregnant women and children. See, Using Breath Tests Wisely in a Gastroenterology Practice: An Evidence-Based Review of Indications and Pitfalls in Interpretation, Romagnuolo, et al., Am J Gastroenterology 97:1113-1126 (2002).
A further difficulty arising with the UBT is the high cost of 13C-urea, as well as the cost and operational expenses of instruments to detect exhaled 13CO2.
To solve this shortcoming, the present invention departs from detection of 13CO2 by using unlabeled urea as a substrate, detecting ammonia in breath instead of CO2. The present invention provides an ammonia-specific nanosensor and provides a simple, inexpensive hand-held device for the detection of breath NH3.
Accordingly, the present invention provides a highly accurate, economical, easy to operate, portable and sufficiently sensitive medical device for diagnosis of H. Pylori. The present invention departs from detection of 13CO2 and provides a simplified assay that uses lower cost unlabeled urea as a substrate.